This invention relates to electrical contact members and, more particularly, to an improved edge contact member for use in an integrated circuit chip burn-in connector.
As part of the manufacturing process, integrated circuit chips typically go through a process of burn-in testing. To accomplish this testing, a special burn-in connector is utilized. This connector typically undergoes a large number of insertion/removal cycles of integrated circuit chips. Accordingly, the connector structure and the contact members in particular have to be designed to accommodate the large number of cycles.
Integrated circuit chips are typically manufactured with tin plated leads. This results in a contact physics or metallurgy problem. It is known that when two dissimilar metals come into rubbing contact, a thin layer of the softer metal will be deposited on the harder metal. Therefore, if the connector contact is gold plated, at the first insertion of an integrated circuit chip, a small amount of tin from the chip leads will be transferred as an extremely thin layer onto the gold of the connector contacts. By its very nature, a thin layer of this type is very stressed. The tin will then attempt to reduce its stress state by reacting with an available gas in its vicinity. Such gas will typically be oxygen, but it may also be sulphur, iodine, chlorine, etc. This reaction will result in the formation of a compound, which may be termed, using literary license, an "oxide layer". Irrespective of its exact chemical makeup, this layer either is non-conductive or semi-conductive and, as a result, the electrical resistance of the contact will change from several milliohms to several hundred milliohms, or higher. Accordingly, gold is not a desirable surface material for a contact of the character described herein. An alternative surface material for such a contact which is commonly used is tin plating over nickel. However, such a contact is subject to fretting corrosion (i.e., corrosion due to stress which forms a film on a soft material such as tin), which raises the contact resistance. Accordingly, it is a primary object of this invention to provide an improved electrical contact member for use with a burn-in connector for integrated circuit chips which does not suffer from the aforenoted problems.